1. Field of the Invention
The present invention relates to a communications device, and more particularly, to a communications device capable of simultaneously operating in a dual-band CDMA communications system and a dual-band GSM communications system.
2. Description of the Prior Art
As radio communications technology progresses, mobile phones of small sizes change the way people communicate. The mobile phones provide people an opportunity to exchange information any time anywhere. The prior art developed different mobile communications systems, such as Global System for Mobile communications (GSM), Code Division Multiple Access (CDMA), Wideband Code Division Multiple Access (WCDMA), Personal Digital Cellular (PDC), and Personal Handyphone System (PHS).
The GSM communications system is composed of the GSM communications systems with frequencies of 900 MHz and 1800 MHz. The GSM communications system of 1800 MHz is also named as Digital Cellular System (DCS). The receiving band of the GSM communications system of 900 MHz ranges between 925.2 MHz and 959.8 MHz. The transmission band of the GSM communications system of 900 MHz ranges between 880.2 MHz and 914.8 MHz. The receiving band of the GSM communications system of 1800 MHz ranges between 1805.2 MHz and 1879.8 MHz. The transmission band of the GSM communications system of 1800 MHz ranges between 1710.2 MHz and 1784.8 MHz. Thus, the GSM communications system is also named as the dual-band GSM communications system.
The CDMA communications system is composed of the cellular CDMA communications system of 800 MHz and the Personal Communications Services (PCS) CDMA communications system of 1900 MHz. The receiving band of the cellular CDMA communications system ranges between 869 MHz and 894 MHz. The transmission band of the cellular CDMA communications system ranges between 824 MHz and 849 MHz. The receiving band of the PCS CDMA communications system ranges between 1930 MHz and 1990 MHz. The transmission band of the PCS CDMA communications system ranges between 1850 MHz and 1910 MHz. Thus, the CDMA communications system is also named as the dual-band CDMA communications system.
From the description above, it is known that the frequency bands of the GSM communications system of 900 MHz and the cellular CDMA communications system partly overlap, and the frequency bands of the GSM communications system of 1800 MHz and the PCS CDMA communications system partly overlap. Please refer to FIG. 1 and FIG. 2. FIG. 1 is a diagram illustrating the overlapping frequency band of the GSM communications system of 900 MHz and the cellular CDMA communications system. FIG. 2 is a diagram illustrating the overlapping frequency band of the GSM communications system of 1800 MHz and the PCS CDMA communications system. In FIG. 1 and FIG. 2, the shadowed area represents the overlapping frequency band. Because of the overlapping frequency bands in FIG. 1 and FIG. 2, the prior art cannot provide mobile phones simultaneously operating in the GSM communications system of 900 MHz and the cellular CDMA communications system, or mobile phones simultaneously operating in the GSM communications system of 1800 MHz and the PCS CDMA communications system.